Compression of test pattern response data into signatures is a well-established technique that has been used for decades, especially for Logic Built-In Self Test (LBIST). More recently it has been used as part of a more general approach for test data compression to save data volume and test time. For example, Cadence Test products available from Cadence Design Systems, Inc., headquartered in San Jose, Calif., use on-product signature compression to reduce both test data volume and test time.
When Multiple Input Signature Registers (MISRs) are used to compress response , data, performing diagnostics using just the failing MISR signatures is impossible. To allow diagnostics to work, the traditional solution is to re-apply a failing test up to the point where the response data would be serially compressed into the MISR, but instead, switch scan configurations so that the internal response data can be fully scanned off chip into the tester for later diagnostic analysis. Although reasonable and used by Cadence for OPMISR, OPMISR+, and SmartBIST compression methods, this approach requires dumping all response bits for a failing test into tester buffers or storing the full set of expected values on the tester and then storing only the observed differences in the tester fail buffer memory. Either way requires the tester to have a large response data repository.
In view of the foregoing, a need exists for an improved system and method for performing logic test failure diagnosis that overcomes the aforementioned obstacles and deficiencies of currently-available hardware test and diagnostic systems.
It should be noted that the figures are not drawn to scale and that elements of similar structures or functions are generally represented by like reference numerals for illustrative purposes throughout the figures. It also should be noted that the figures are only intended to facilitate the description of the preferred embodiments of the present invention. The figures do not describe every aspect of the present invention and do not limit the scope of the invention.